Now why would we go through the trouble of applying a white coat? There are two major reasons:
Energy efficiency and global warming. A white coat can reflect up to 80 percent of solar radiation, reducing overall planet temperature but more immediately reducing building, neighborhood and city temperature. One white roof is small local block against the urban "heat island" effect and many of them can have wide impact. The white roof will reduce the internal temperature and the need for air conditioning, which in turn reduces the electricity usage and so forth. (There is some question about possible heat loss effect of a white roof in winter. At St. Louis' latitude the sun's rays are vertical in the summer and at a low slant in the winter, so the available winter solar heat is much less than the summer heat. At other latitudes, a white roof might not be of such benefit as here and points southward.)
Longevity of the roof. An elastomeric coat will block ultraviolet rays that slowly break down asphalt roofing. Coats should be reapplied every 10 years or sooner if needed. With timely reapplication, the coverage can extend the life of the roof to 40-50 years, reducing cost as well as waste of nonrenewable roofing materials.
While the mason had the scaffolding set up, we used his pulley to hoist up the 5 gallon buckets of coating. We used five $72 buckets of Henry Solarflex 287, which completely covered our 1300 square foot roof. When the scaffolding was down, we used a tall ladder for travel to the roof.
Working with a friend, we spent about eight hours washing the roof and applying the coat. Since we had just had masonry work, the roof was dirty and required over two hours of scrubbing. The mod-bit roof dried quickly, however. We applied the coat with a 4" brush on the parapet sides and 9" rough rollers on the roof. We avoided a few new flashing repairs made around the rebuilt chimneys.